Prior art tokamak fusion reactor (TFR) concepts were directed to large machines with blanket and shield elements positioned in between the plasma fusion region of the TFR and the large superconducting toroidal field (TF) coils. In U.S. Pat. Nos. 4,367,193and 4,363,775, there is disclosed a small machine with the blanket means positioned external to the normally conducting TF coil assembly. It is known in the art that such blankets can advantageously use the neutrons generated in the fusion plasma to breed new fuel, to produce thermal energy and to create additional energetic reactions. This invention is directed to those TFRs utilizing external blankets (XBTFR) such as those disclosed in the commonly assigned U.S. Patent applications referred to above.
In the case where a TFR uses the deuterium-tritium (d,t) reaction, approximately 80% of the energy output is in the form of the kinetic energy of fast neutrons. In the small machine referred to in the above-referenced U.S. patents, the TF coil is exposed to the flux. The neutron radiation damage and heat loads preclude the use of superconducting materials for the TF coils in this small machine design. Applicants have found that the materials used in the TF coils must have both high electrical conductivity to carry the high currents necessary to generate the TF and also high tensile strength to withstand the forces accompanying the strong magnetic fields. Applicants have found that TF coils of high electrical conductivity can be made from high strength copper alloys. However inasmuch as in the small TFR design, the TF coil surrounds the plasma region, the neutrons created as a result of the fusion reactions must pass through it. In this regard, it has been found by Applicants that copper and copper alloy coils will absorb a considerable fraction of the neutrons and that those that do emerge without being absorbed in the TF coils will have lost much of their kinetic energy in the copper or copper alloy.
While it is a feature of the TFR design disclosed in the above-referenced U.S. patents to remove the energy deposited in the TF coils and recover it as useful heat, energetic neutrons are far too valuable for breeding fuel for fusion and fission reactors and for generating high temperature heat in the blanket to be used merely as a source of low temperature heat in the TF coils.
Applicants have also found that one of the consequences of the TFR geometry is that the current density and mechanical stresses imposed on the TF coils are much greater in the region of the inner part of the TF coil, the region nearest the center or the main axis of the machine. Another consequence of the XBTFR geometry is that most of the neutrons generated in the fusion plasma exit through the outer part of the TF coil or the region farthest from the central or main axis of the TFR.